This is a Phase II, Randomized, Partially Double Blind, Six Arm Study. Subjects will be randomized twice at entry into the study. Initially, subjects will be randomized to either the ddI or d4T limbs and then within a limb, will be randomized a second time into one of three study arms. Randomiztion into one of the three study arms of each limb will occur in a 1.5:1.5:1 ratio. This randomization ratio is chosen in order to minimize sample size while retaining power to detect a 0.5-log10 difference between arms at Weeks 24 and 48. At study week 24, subjects on monotherapy will have lamivudine (3TC) added to their regimen in a blinded fashion. Subjects who begin the study on combination therapy will remain on that same combination therapy. To simplify dosing, blinding of limb assignment will not occur, but randomization into the arms of each of the limbs will be blinded.